Distribution and Medicinal Usage
Sophora flavescens, (Kurara) belongs to the family Leguminosae and is distributed in Mongolia, the eastern part of Russia, China, Korea, and Japan. The dry roots of this plant have been used as antipyretic analgesic, bitter stomachic, anthelmintic, as an external preparation for eczema, and an agricultural insecticide in China and Japan (). A number of interesting pharmacological activities were reported for alkaloids and the extracts of this plant, for example, a diuretic activity, an antimicrobial activity, an antiarrhythmic activity (), and an antiulcerogenic activity ().
History of Alkaloid Study
In 1889, Nagai first reported the isolation of matrine, a main alkaloidal constituent, from the dry roots of Sophora flavescens. The skeletal structure of matrine was proposed by Tsuda (), and subsequently it was proved by synthetic studies (). The absolute structure of (+)-matrine was confirmed by Okuda et al. (). Several new alkaloids related to matrine were isolated and their structures were determined from Sophora flavescens and related plant species in the course of our continued studies of lupin alkaloids (). The biosynthesis of matrine was also investigated in intact plants of Sophora flavescens by Shibata and Sankawa () and in related species ().The carbon skeleton of matrine () is constructed from lysine () via a diiminium cation intermediate (), which is electrostatically equivalent to () for biosynthesis of lupanine ().
Furuya and Ikuta () established callus culture of Sophora flavescens and demonstrated that the callus produced the flavonoids (-)-maackiain and pterocarpin. The production of lupin alkaloids in cell culture of Sophora flavescens was recently reported () by using green callus and multiple shoots. The greening-induced production of lupin alkaloid was also observed in tissue culture of Thermopsis lupinoides (), which is also used as a source plant in Chinese traditional medicine ().
In Sophora flavescens it was indicated that the biosynthesis of matrine is closely correlated to the formation of chloroplasts in the cells () as well as in Lupinus species (). Matrine and lupanine are assumed to be the initial metabolites in the biosynthetic pathways of matrine-type and anagyrine-type alkaloids, respectively (). The finding that matrine or lupanine was the only alkaloid produced in undifferentiated callus tissues may suggest that the biotransformation activity responsible for matrine and lupanine is suppressed in the undiflerentiated tissue.
The differentiated multiple shoots in which root organ is not developed synthesized 5,6-dehydrolupanine and anagyrine as well as matrine in higher concentrations than in green callus. These findings suggest that the expression of biosynthetic activities for matrine-type and anagyrine-type alkaloids, which have different modes of formation of their carbon skeletons, are differently controlled during the developmental stages of Sophora flavescens cells. The occurrence of 5,6-dehydrolupanine, in particular, is intriguing from a biosynthetic point of view. 5,6-Dehydrolupanine is postulated to be a key intermediate for biosynthesis of anagyrine-type alkaloids (). However, 5,6-dehydrolupanine is present in only trace amounts in differentiated plants, although the concentrations of matrine and anagyrine are, for example, 1-2 mg/g of fresh weight of seeds. The substantial accumulation of 5,6-dehydrolupanine, besides anagyrine, in the multiple shoots indicates that the biosynthetic activity to anagyrine via 5,6-dehydrolupanine is expressed in the multiple shoots.
The dry root of Sophora flavescens is used as a crude drug. A high concentration of matrine N-oxide is normally detected in this dry root. However, in the cultured tissues, matrine N-oxide could not be detected. Thus, it is possible that the root organ is responsible for storage and biotransformation of lupin alkaloids produced in leaves, suggesting sectionizing the functions for secondary metabolism in plants ().
Selections from the book: “Medicinal and Aromatic Plants V”, 1993.